1. Field of the Invention
The present invention relates to an overhead conveying vehicle, particularly to an overhead conveying vehicle arranged to convey a suspended article having a lid that is removably provided on a side surface thereof.
2. Description of the Related Art
An overhead conveying vehicle system including an overhead conveying vehicle arranged to travel along a traveling rail provided on a ceiling is conventionally used to carry articles in a cleanroom (e.g., in a semiconductor manufacturing plant), where dust production is a problem.
The overhead conveying vehicle includes a traveling section arranged to travel along the traveling rail, an article containing section arranged to contain an article, and a hoist capable of raising and lowering the article. The hoist has a chuck for clasping the article, a belt capable of moving the chuck up and down, and a belt driving mechanism that can reel out and wind in the belt.
An example of an article conveyed by the overhead conveying vehicle in a cleanroom is a FOUP (Front Opening Unified Pod). A FOUP is a wafer storage pod that can be sealed. FOUPs ensure the cleanness of wafers and enable the miniaturization that accompanies larger wafer sizes to be accommodated. A FOUP includes a cassette and a lid for closing an opening on a side of the cassette. The lid serves to prevent particles from entering the cassette and to position the wafers inside the cassette.
The overhead conveying vehicle travels with the FOUP having been raised by the hoist and placed in the containing section. When it comes in front of a manufacturing apparatus, the overhead conveying vehicle lowers the FOUP with the hoist and places the FOUP on a table of a load port. After the FOUP is placed onto the table, it is docked with the opening of the manufacturing apparatus. Then, a FOUP opener removes the lid from the cassette of the FOUP and pulls the lid into the apparatus. The wafers are then carried into the semiconductor manufacturing apparatus and a prescribed process is executed. After the process, the wafers are returned into the FOUP and the lid is put back to close the FOUP. The overhead conveying vehicle uses the hoist to hold the FOUP resting on the table of the load port of the manufacturing apparatus and raise the FOUP to a containment position. The overhead conveying vehicle then contains the FOUP and starts traveling. In this way, the overhead conveying vehicle moves the FOUP between load ports.
With an overhead conveying vehicle system, there are times when automatic guide vehicles pass under the traveling rail and when workers move and work under the rail. If the lid drops from the FOUP at such a time, the worker could be injured or another device could be damaged. Therefore, a configuration in which a lid drop preventing member is provided on the overhead conveying vehicle has been proposed (e.g., see Japanese Laid-open Patent Publication No. 2004-277066 (U.S. Pat. No. 3,885,232)).
The lid drop preventing member presented in Japanese Laid-open Patent Publication No. 2004-277066 (U.S. Pat. No. 3,885,232) is fastened to a hoist chuck such that it can move sideways with the hoist chuck, but cannot move in another direction. Consequently, there is a possibility that the hoist chuck or the FOUP will be in contact with the lid drop preventing member when the FOUP is lowered from the containment position or moved upward from a loading port. In particular, when the FOUP rocks while being raised, the FOUP can easily collide against the lid drop preventing member. If such a collision occurs, the overhead conveying vehicle will shake and the wafers inside the FOUP will undergo a physical shock due to the shaking. It is also possible for the shaken traveling vehicle to strike another traveling vehicle.